The present invention relates broadly to surgical repair or replacement of diseased, or damaged, joints of the human body, and more particularly to cement plugs for sealing the medullary canal of a bone to prevent cement travel therepast.
Replacement of diseased, or damaged, human joints by prosthetic devices is well known. Such prosthetic devices are used to replace defective finger joints, elbow joints, knee joints and hip joints. Frequently, these prosthetic devices include an elongated stem that is inserted into the medullary canal of the bone adjacent to the resected joint. In a hip joint replacement, for example, the elongated stem of a hardened, biologically acceptable metal material is inserted into the medullary canal of the femur, and the ball, or head, of the prosthesis fits into a properly prepared socket in the pelvis of the patient. A plug is positioned within the medullary canal. The plug serves as a barrier to the flow of the cement, beyond a predetermined depth, so that the cement can secure the elongated stem of the prosthetic device at the desired depth within the canal. The cement is typically a curable acrylic polymer cement, such as polymethylmethacrylate, which exhibits a tendency to flow past the plug. Such tendency is exacerbated by the need to inject the cement into the medullary canal under pressure.
Diverse cement plugs for blocking the medullary canal, and thus providing a stable base for the elongated stem of a prosthetic device or the like, are shown in the patented prior art. To illustrate, U.S. Pat. No. 4,302,855, granted Dec. 1, 1981, to Alfred B. Swanson, discloses a bone plug 10 for plugging the medullary canal of a bone to restrict the flow of cement to affix a prosthesis. The bone plug comprises a resilient body of medical grade material, such as silicone polymer rubber. The body has a smooth, blunt, round nose 12, a midportion 14 joined to the nose and having a toroidal shape, and an upper, open ended portion 16 joined to the midportion and defining a recess 18. The upper, open ended portion is generally frusto-conical in shape, and further defines a plurality of circumferentially spaced petal-like elements 36. A manual instrument (FIG. 6) is used to insert the properly sized bone plug, to the correct depth, within the medullary canal, prior to the introduction of acrylic cement, under pressure.
U.S. Pat. No. 4,344,190, granted Aug. 17, 1982 to Alan J. C. Lee and Robin S. M. Ling, discloses an implant that is adapted to locate a hip prosthesis. A push-fit plug 12 fits into the medullary canal 18, and prevents cement from penetrating down the canal. The plug may be formed of a biodegradable material, may have serrations about its midsection for enhanced gripping ability, and may be tapered or conical at its upper end 16. An implant 22 is located above plug 12 and is retained in fixed position by pressurized cement 24.
U.S. Pat. No. 4,276,659, granted July 7, 1981, to Kevin Hardinge, discloses another medullary canal plug. The plug comprises a substantially hemispherical center 10 with a plurality of individual leaves 11 radiating outwardly from the center. The adjacent edges 12 of the leaves are angularly inclined relative to the faces to facilitate the partial overlapping of the leaves, when moved from a planar disposition (shown in FIG. 2) to a frusto-conical position (shown in FIG. 3) during insertion into the medullary canal 15.
U.S. Pat. No. 4,447,915, granted May 15, 1984 to Berhard G. Weber, discloses a medullary canal plug comprising: a deformable and expandable cup-shaped outer body 1 having a jacket formed of a number of segments 3, and a conical expansion body 10 which is pulled, or drawn, into the outer body in order to expand same. The expansion of the outer body causes barb-like anchoring elements 4 to hook into the inner wall 32 of a bone 30. The two bodies 1, 10 are permanently secured together, via serrations 5, 11 on the inside of outer body 10 and on the outside of the expansion body. A tool 20 with an elongated spindle 21 passes axially through the outer body 1 to engage a central bore in the expansion body and draw such body upwardly into the lower, open end of the outer body 1.
U.S. Pat. No. 4,245,359, granted Jan. 20, 1981, to Karl-Gerhard Stuhmet, discloses a plug 3 that is made of a plastic material and functions as a cement barrier for openings produced by an operative procedure in medullated bones 1. The plug is clamped between the side walls of the opening in the bone by elastic flanges 6, 8, which prevent bone cement from escaping downwardly upon inserting a medullary stem. U.S. Pat. No. 4,686,973, granted Aug. 18, 1987 to Elden E. Frisch, discloses an inflatable bone plug that is inflated with a biocompatible fluid, and is deflated in a controlled manner, after the cement hardens. The bone plug may be formed of a container of a silicone elastomer permeable to carbon dioxide gas.
U.S. Pat. No. 4,011,602, granted Mar. 15, 1977, to E. F. Rybicki et al, discloses a porous, expandable device for attachment to bone tissue. The device includes a body member that is slit from opposite ends, and receives a cylinder member 22 therein in response to actuation of threaded bolt 26.
Yet other bone plugs are shown in U.S. Pat. No. 4,293,962, granted Oct. 13, 1981 to Robert L. Fuson; U.S. Pat. No. 4,627,434, granted Dec. 9, 1986, to William M. Murray; and U.S. Pat. No. 4,337,773, granted July 6, 1982, to D. D. Raftopoulus et al.
Despite the variety of bone plugs, which are also known as cement plugs, long term follow-up studies of replacements and repairs have shown that the holding power of conventional plugs has been less than anticipated. Cement migration and leakage has been found to be a persistent problem. Consequently, the failure rate of the surgical repairs and/or replacements for different joints, or at the very least, the loosening of such joints over time, has been far higher than anticipated. Thus, the need for a simple, inexpensive, biocompatible, adjustable cement plug that will fit securely within canals of various sizes and yet function effectively, over prolonged periods of time, remains, at best, only partially met.